1. Field of the Invention
The present invention relates generally to free-space optical communication, and more specifically to alignment tracking control in free-space optical networks.
2. Discussion of the Related Art
For digital data communications, optical media offers many advantages compared to wired and RF media. Large amounts of information can be encoded into optical signals, and the optical signals are not subject to many of the interference and noise problems that adversely influence wired electrical communications and RF broadcasts. Furthermore, optical techniques are theoretically capable of encoding up to three orders of magnitude more information than can be practically encoded onto wired electrical or broadcast RF communications, thus offering the advantage of carrying much more information.
Fiber optics is the most prevalent type of conductors used to carry optical signals. An enormous amount of information can be transmitted over fiber optic conductors. A major disadvantage of fiber optic conductors, however, is that they must be physically installed.
Free-space atmospheric links have also been employed to communicate information optically. A free-space link extends in a line of sight path between the optical transmitter and the optical receiver. Free-space optical links have the advantage of not requiring a physical installation of conductors. Free-space optical links also offer the advantage of higher selectivity in eliminating sources of interference, because the optical links can be focused directly between the optical transmitters and receivers, better than RF communications, which are broadcasted with far less directionality. Therefore, any adverse influences not present in this direct, line-of-sight path or link will not interfere with optical signals communicated.
Despite their advantages, the quality and power of the optical signal transmitted depends significantly on the alignment between cooperating link heads.
It is with respect to these and other background information factors relevant to the field of optical communications that the present invention has evolved.